1. Field of the Invention
The present invention relates to an image forming apparatus (e.g., a copier, a printer, a facsimile machine, a multifunction machine), a fixing apparatus and a heating member that are mounted in the image forming apparatus.
2. Description of the Related Art
Conventionally, there is a known method in which a fixing belt, spanning across plural roller members, is used as a fixing member in an image forming apparatus (e.g., copier, printer) (for example, see Japanese Laid-Open Patent Application No. 11-2982). This type of image forming apparatus includes, for example, a fixing belt (endless belt) used as a fixing member, plural roller members around and between which the fixing belt spans, a heater installed in one of the plural roller members, and a pressure roller (pressing member). The heater heats the fixing belt via its corresponding roller member. Then, a recording medium is conveyed to a nipping part between the fixing belt and the pressure roller, so that a toner image can be fixed onto the recording medium by heat and pressure applied at the nipping part.
Another fixing apparatus (on-demand type fixing apparatus) requiring a short warm-up time is disclosed in Japanese Laid-Open Patent Application No. 2002-6656. The on-demand type fixing apparatus includes, for example, a fixing film (endless film) used as a fixing member, a pressure roller (pressing member), and a heater (e.g., ceramic heater). The ceramic heater is installed in the fixing film. The ceramic heater forms a nipping part by contacting the pressure roller via the fixing film. The ceramic heater is configured to heat the fixing film. Accordingly, a recording medium is conveyed to the nipping part, so that a toner image can be fixed onto the recording medium by heat and pressure applied at the nipping part.
Although the fixing apparatus of Japanese Laid-Open Patent Application No. 11-2982 may be suitable for realizing faster operations compared to an apparatus using a fixing roller, this fixing apparatus has limits in shortening a warm-up time (time required for reaching a temperature for performing a printing operation) or a first print time (time required for preparing and performing a printing operation starting from receipt of a print request and ending when a printed paper is discharged).
On the other hand, the fixing apparatus disclosed in Japanese Laid-Open Patent Application No. 2002-6656 enables shortening of the warm-up time and the first print time due to its reduced heat capacity. Furthermore, size reduction can be realized with this fixing apparatus. However, because this fixing apparatus locally heats the nipping part of the fixing film only, areas other than the fixing film are not sufficiently heated. Thus, the rotation of the fixing film causes the fixing film to become coldest at the mouth of the nipping part. This leads to poor fixing results. With this fixing apparatus, more heat is released from the fixing film at areas other than the nipping part as the rotation of the fixing film becomes faster.
In order to resolve the above-described problems, there is a method of providing a pipe-like heating member formed of a thermally conductive material in a manner facing an inner peripheral surface of an endless fixing member (e.g., endless fixing belt, endless fixing film), so that the entire fixing member can be uniformly and sufficiently heated by directly or indirectly heating the heating member.
In order to improve the heating efficiency of the fixing member, it is desired to make the pipe-like heating member (thermally conductive metal material) as thin as possible. However, there are limits in precisely fabricating such a thin pipe-like heating member by a cutting process. For example, the rigidity of the heating member may decrease as the cutting process progresses. The heating member having such a decreased rigidity may be deformed by the chucking force applied by a processing machine or bent during a cutting process. This makes it difficult to fabricate the heating member with a uniform thickness.
Particularly, in a case where an area of the heating member corresponding to the nipping part is formed in a flat shape or a recessed shape for improving the property of separating a recording medium delivered from the nipping part, it is difficult to perform a precise cutting process on the heating member. In forming the area in a flat or recessed shape, it is also necessary to perform subsequent additional processes on the heating member. This results in an increase of manufacturing costs. In other words, fabricating a precise inexpensive heating member becomes more difficult as the heating member becomes thinner.